1. Field of the Invention
The present invention relates to mineral dressing and, more particularly, to flotation machines.
The invention is readily applicable for use in ore-mining, coke- and coal-mining and other related industries.
Treatment of slimes, carried out on an ever growing scale, as well as the modern trend toward flotation of diluted pulps, requires the provision of flotation machines of large capacity (not less than 800 m.sup.3 /h).
Such a rate of operation is possible to achieve in large-capacity cells of 8 to 11 m.sup.3, and even of 17 m.sup.3. The employment of large-capacity cells enables their production efficiency to be enhanced, power consumption to be reduced, and capital and operating costs to be reduced ("Equipment for Flotation Machines", Report at All-Union Seminar on Science and Technology, Apr. 18-20, 1972, the city of Voroshilovgrad, pp. 33-34).
Large-capacity flotation machines, however, are not free from disadvantages, for example, such as nonuniform aeration of pulp throughout the cell volume, insufficient recirculation and slow speed of pulp streams, and delays in the removal of froth, particularly, from the central part of the cell.
2. Description of the Prior Art
For example, there is known a flotation machine (cf. USSR Inventor's Certificate No. 400,368, cl. B03 D I/24), in which two horizontal aerators are mounted on the outside with the purpose of increasing the pulp load capacity. In this machine, therefore, the aeration zone and the flotation zone are separated from one another.
When put in operation, the flotation machine of the Inventor's Certificate referred to above has not exhibited high production efficiency, but revealed low performance characteristics due to the minimum recirculation of pulp and the insufficient amount of sucked-in air. In the course of operation air is accumulated in the upper part of the cell, which is then periodically discharged in substantial portions and thus destroys the froth layer. USSR Inventor's Certificate No. 366,889 discloses a flotation machine which has two horizontal aerators compartmented by vertical partitions. This machine suffers basically from the same disadvantages as the previously described one. The pulp streams circulating in the cell are not efficient enough, the directional flow of pulp in the lower part of the cell is almost nonexistent. Therefore, the machine is not highly efficient and is complicated in construction.
There is also known a flotation machine (cf. "Modern Foreign-Made Flotation Machines", Moscow Publishers, 1971, pp. 9-25), which comprises a plurality of flotation cells arranged in series, each being provided with an inlet opening for feed to pass there-through and with outlet discharge compartments combined in units and arranged in stages. The units are connected by means of boxes intended to adjust the level of pulp in the compartments of separate units. Mounted in each compartment are four impellers with stabilizers. The stabilizers are made in the form of square-shaped plates each fitted with a central opening to receive the impeller. Fixed on the surface of the plate are radially arranged blades. The periphery of each opening in the plate passes over internal edges of the vertical blades. Intermediate external surfaces of the plate and the walls of each cell, as well as between adjacent plates, there are provided gaps adapted to ensure pulp circulation. The main disadvantage of this prior-art machine is that the streams of pulp are flown in disorderly manner in the cell provided with four impellers causing pulp swirls which result in froth breakage. With the impeller being arranged on the plate, radial streams are created thereon, which overlap the streams created by the impeller located nearby. In the space under the plate, however, the center-bound streams are nonexistant at all. In addition, the rate and direction of the recirculating flows are impossible to regulate in the above-described machine. All the disadvantages cited above render the prior-art flotation machine inefficient in operation.
U.S. Pat. No. 3,647,066 (or Federal Republic of Germany Pat. No. 1,533,570) describes a flotation machine which comprises a plurality of cells arranged in series and combined in units, each of which may accommodate two or four aerators set in strict symmetry relative to the walls of each cell. The machine also incorporates a froth-removing device, a feed compartment and a free-circulation compartment, discharging launders, and a stator means made in the form of a square plate with an opening for an aerator. Arranged on the plate around the aerator are stator plates.
The disadvantage of the above-described machine is that there is substantial swirling of pulp created over the cell surface, which results in the froth being demineralized. The reason for this is that with two impellers being arranged in one cell transversely to the pulp flow, or with four impellers disposed transversely and longitudinally to the pulp flow, the streams of the rejected liquid from two different impellers tend to overlap. This being the case (V. G. Geiff ed al. "Hydraulics and Hydraulic Drive", "Nedra", Moscow Publishers, 1970, pp. 118-121), a combined flow is created which is bound toward the bottom of the cell and toward the froth layer. This, in turn, brings about froth breakage.
Another disadvantage of this machine is insufficient and uncontrolled recirculation of pulp.
It is known (cf. "issledovanie Protsessa Aeratsii V Mekhanicheskikh Flotatsionnykh Machinakh"/"A Study of Aeration in Mechanical Flotation Machines", "Gorniy Journal" No. 2, 1969, pp. 151-161 that the rate of pulp circulation has direct bearing on the flotation process. The higher the feed rate of pulp, the higher is the rate of its circulation. To ensure good conditions for carrying out the flotation process with changes in the feed rate and in the content of solids, the rate of circulation should be regulated within a broad range. The direction and rate of circulation should be predetermined. In the machine disclosed in U.S. Pat. No. 3,647,066 these variables are impossible to control, and, therefore, the direction of pulp streams in the cell is chaotic.
In addition, the above-mentioned machine has a disadvantage which resides in the impossibility of timely removing the froth accumulated in the central part of the cell. The machine is designed so that the removal of froth from the central part of the cell is carried out with the aid of a trough positioned along the longitudinal axis of the machine.
When four impellers are arranged in the cell, the extent of froth removal in the interspace between the impellers is poor, which results in froth buildup in this zone. Moreover, there is no removal of froth from the area disposed between the path, along which pass the pulp streams, and the shafts of the impellers.
From the above it follows that the prior-art flotation machines described above fail to provide effective flotation of large amounts of pulp.